Ink, ink-jet recording process and apparatus making use of the same

ABSTRACT

Provided is an ink comprising a compound having at least one carbonyl group and a hydrazide compound selected from the group consisting of a styrene-maleic acid resin having at least two hydrazide groups, a polyacrylic acid having at least two hydrazide groups and a compound represented by the formula ##STR1## wherein R represents (CH 2 ) n  or C 6  H 4 , where n is an integer of 0 to 10, or the formula ##STR2##

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an ink suited for ink-jet printers, andalso to an ink-jet recording process and apparatus that make a record onpaper by causing ink to fly from orifices of a recording head by theaction of energy, preferably heat energy. More particularly, it relatesto an ink-jet recording process and apparatus that make a record onnon-coated paper such as paper for copying, paper for reporting,notepaper, letter paper, bond paper and computer printout paper(continuous business forms) commonly used in offices and homes.

2. Related Background Art

Ink-jet recording systems have the advantages that they make less noisein the course of recording and a recorded image with a high resolutioncan be obtained at a high speed because of use of a highly integratedhead. Inks used in such ink-jet recording systems are those prepared bydissolving various kinds of water-soluble dyes in water or in a mixedsolution of water and an organic solvent.

When the water-soluble dyes are used, however, light fastness ofrecorded images is often questioned because such water-soluble dyes havepoor light fastness by nature.

Water fastness of recorded images is also often questioned because thedye is water-soluble. More specifically, if recorded images become wetwith rain, sweat, or water from food and drink, they may become blurredor disappear.

Meanwhile, light fastness and water fastness are similarly questionedalso in writing utensils such as ball-point pens because water-solubledyes are mainly used, and various water-based pigment inks for writingutensils have been proposed so that such problems can be settled.Examples of studies on dispersion stability, prevention of inksolidification at pen points and prevention of ball wear of ballpointpens for the purpose of putting water-based pigment inks into practicaluse are seen in Japanese Patent Application Laid-Open No. 58-80368, No.61-200182, No. 61-247774, No. 61-272278, No. 62-568, No. 62-101671, No.62-101672, No. 1-249869, No. 1-301760, etc. Recently, ball-point pens ormarkers making use of water-based pigment inks have become commerciallyavailable.

Also ink-jet recording inks making use of water-based pigment inks,pigment inks making use of specific water-soluble solvent and polymericdispersant are proposed in Japanese Patent Application Laid-Open No.56-147859 and No. 56-147860. Inks making use of a pigment and a dye incombination are also proposed in Japanese Patent Application Laid-OpenNo. 4-57859 and No. 4-57860.

In ink-jet recording, it is very important for non-volatile componentsin the ink to rapidly cohere after ejection onto the recording paper.When, however, the conventional water-based pigment inks are used inink-jet recording, the non-volatile components which have cohered onrecording paper are kept present on the recording paper as a solidmaterial after the ink has been fixed thereon. Hence, there has been theproblem that print surfaces stain when strongly rubbed or when tracedwith a highlighter pen (fluorescent-ink pen).

When conventional inks are used to make a record by ink-jet recording onplain paper on which no particular ink-receiving layer is formed, therealso has been the problem that leathering may occur, though it differsmore or less depending on composition. Accordingly, in order to preventthe feathering, it is proposed to add a highly viscous solvent to ink.The feathering can be prevented by increasing the ink viscosity.However, a highly viscous organic solvent must be added in a largequantity for such purpose, so that the ink comes to have an excessivelyhigh viscosity, which brings about the problem that the ejection of inkmay become unstable because of a decrease in ejection speed of the inkfrom nozzles or a decrease in surface tension. There still also has beenthe problem that the degree of print density or feathering may differdepending on the types of recording paper.

As an attempt to solve such problems, Japanese Patent Publication No.60-500540 and Japanese Patent Application Laid-open No. 63-159485disclose techniques in which iodine or the like is added to ink toimprove the quality level of prints on a specific recording paper. Thetechniques disclosed in these publications, however, are not effectivefor a great variety of recording paper.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide an inkthat can be free from any irregular print quality level due todifferences in the types of recording paper and can satisfy fixing speedand rub-off fastness, and also thereby obtain stable recorded imageswithout decreasing print density.

Another object of the present invention is to provide an ink thatenables blurring-free recording on all sorts of recording paper withoutexcessively increasing the viscosity of the ink and also has superiorrecording performances in variety, and an ink-jet recording process andapparatus making use of the ink; more specifically, to provide an inkthat has solved the problems of blurring of ink and slow-drying ofrecorded matter that may occur when recording is performed on non-coatedpaper, what is called plain paper, such as paper for copying, paper forreporting, notepaper, letter paper, bond paper and computer printoutpaper commonly used in offices and so forth.

A still another object of the present invention is to provide an inkthat is very safe when used in offices and homes.

The above objects of the present invention can be achieved by theinvention as described below.

The present invention is an ink comprising a hydrazide compound selectedfrom the group consisting of a compound represented by the followingFormula (I) or (II), a styrene-maleic acid resin having at least twohydrazide groups and a polyacrylic acid having at least two hydrazidegroups, and a compound having at least one carbonyl group. ##STR3##wherein R represents (CH₂)_(n) or C₆ H₄, where n is an integer of 0 to10. ##STR4##

The present invention also provides an ink comprising a water-solubleresin having an oxazolyl group or a fine particle having oxazolyl groupsadsorbed on its outer surface, and a compound having at least onecarbonyl group.

The present invention also provides an ink-jet recording processcomprising ejecting an ink from an orifice according to recordingsignals to make a record on a recording medium, wherein said ink is theink described above.

The present invention still also provides a recording unit comprising anink holder that holds an ink, and a head assembly for ejecting the inkin the form of ink droplets, wherein said ink is the ink describedabove.

The present invention further provides an ink-jet recording apparatuscomprising a recording head for ejecting ink droplets, an ink cartridgehaving an ink holder that holds an ink, and an ink feeding means forfeeding the ink to the recording head, wherein said ink is the inkdescribed above.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a transverse cross section of an example of a liquid flowpath of a recording head suited for the present invention.

FIG. 1B is a cross section along the line A-B in FIG. 1A.

FIG. 2 is a perspective illustration of an embodiment of a recordinghead having ink ejection orifices in a large number.

FIG. 3 is a perspective illustration of an embodiment of an ink-jetrecording apparatus suited for the present invention.

FIG. 4 is a sectional side elevation to show an embodiment of an inkcartridge.

FIG. 5 is a perspective view to show an embodiment of a recording unit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Preferred Embodiment:(Embodiment in which a hydrazide compound is used)

The present inventors have discovered that, in a water-based pigmentink, use of a compound with a specific structural formula brings aboutan improvement in rub-off fastness of prints and can solve the problemspreviously discussed, while maintaining print quality level, and thushave accomplished the present invention. More specifically, a compoundrepresented by the formula ##STR5## wherein R represents (CH₂)_(n) or C₆H₄, where n is an integer of 0 to 10, or the formula ##STR6## astyrene-maleic acid resin having two or more hydrazide groups and apolyacrylic acid having two or more hydrazide groups (these compoundsare hereinafter generically called a hydrazide compound) have theproperties of uniformly dissolving in an aqueous solution and, oncewater has disappeared, reacting with a compound having a carbonyl group.With utilization of such properties, this hydrazide compound is added ina water-based ink so that it is cross-linked with carbonyl groups of adispersant or the like contained in the ink on recording paper, to forma film of non-volatile components, whereby an improvement in rub-offfastness of prints can be achieved. Moreover, the cross-linking reactionuniformly takes place without regard to the types of paper, and henceany dependence of print quality on recording paper can be eliminated.

The present inventors also made extensive studies on a variety of inkcompositions so that blurring-free properties, drying performance andpenetrability of ink on plain paper can be improved. As a result, theyhave discovered that the above hydrazide compounds bring about goodresults against blurring, also have no ill effect on the prevention ofclogging and also have no safety problem, promising high reliability.They have thus accomplished the present invention.

More specifically, according to research made by the present inventors,the use of surface active agents employed in conventional inks makes itdifficult to perform stable recording with regard to the blurring andpenetrability of ink on plain paper, because of mingled results some ofwhich are good and some not. On the other hand, the use of the hydrazidecompound can bring about very good results such that stable recordingwith less difference in quality depending on the types of recordingpaper can be achieved also when used in combination with a penetrantsuch as a surface active agent.

The reason therefor is that the hydrazide compounds have the propertiesof uniformly dissolving in an aqueous solution and, once water hasdisappeared, reacting with a dye having a carbonyl group. Withutilization of such properties, the hydrazide compound is added in awater-based ink so that it is cross-linked with the dye on the recordingpaper, whereby any dependence of print quality level on recording papercan be eliminated and also fixing speed can be improved.

Components that constitute the ink of the present invention will bedescribed below.

As a first ink according to the first embodiment of the ink of thepresent invention, the ink comprises a hydrazide compound, a pigment, anaqueous medium, and a water-soluble resin having a carbonyl group as thecompound having at least one carbonyl group.

There are no particular limitations on the pigment so long as it cansatisfy the functions required in conventional ink-jet recording inks.Particularly preferred examples thereof are shown below.

Carbon black used in black inks may preferably be carbon black producedby the furnace process or the channel process, having a primary particlediameter of from 15 to 40 mμ, a specific surface area of from 50 to 300m² /g as measured by the BET method, a DBP oil absorption of from 40 to150 ml/100 g, a volatile component of from 0.5 to 10% and a pH value offrom 2 to 9. For example, it is preferable to use commercially availableproducts such as No.2300, No.900, MCF88, No.33, No.40, No.45, No.52,MA7, MA8, No.2200B (trade names; available from Mitsubishi ChemicalIndustries Limited), RAVEN1255 (trade name; available from ColumbianChemicals), REGAL400R, REGAL330R, REGAL660R, MOGUL L (trade names;available from Cabot Corp.), and Color Black FW1, Color Black FW18,Color Black S170, Color Black S150, Printex-35, Printex-U (trade names;available from Degussa, Inc.).

Pigments used in yellow inks may include C.I. Pigment Yellow 1, C.I.Pigment Yellow 2, C.I. Pigment Yellow 3, C.I. Pigment Yellow 13, C.I.Pigment Yellow 16 and C.I. Pigment Yellow 83, which can be preferablyused.

Pigments used in magenta inks may include C.I. Pigment Red 5, C.I.Pigment Red 7, C.I. Pigment Red 12, C.I. Pigment Red 48(Ca), C.I.Pigment Red 48(Mn), Pigment Red 57(Ca), C.I. Pigment Red 112 and C.I.Pigment Red 122, which can be preferably used.

Pigments used in cyan inks may include C.I. Pigment Blue 1, C.I. PigmentBlue 2, C.I. Pigment Blue 3, C.I. Pigment Blue 15:3, C.I. Pigment Blue16, C.I. Pigment Blue 22, C.I. Vat Blue 4 and C.I. Vat Blue 6, which canbe preferably used.

The pigment of the first ink of the present invention is by no meanslimited to the above commercially available products, and those newlyproduced may also be used.

The water-soluble resin having carbonyl groups functions as a dispersantof the pigment. Characteristic groups comprising the carbonyl group mayinclude the carbonyl group itself, as well as carboxyl groups, esterbonds, amide bonds, ketone groups and urethane groups. Any water-solubleresins can be used so long as they have a --C═O bond. Those having aweight average molecular weight of from 1,000 to 30,000 are preferred.Those of from 3,000 to 15,000 are more preferred. They specificallyinclude block copolymers, random copolymers and graft copolymers, andsalts thereof, comprised of at least two monomers (at least one of whichis a hydrophilic monomer) selected from the group consisting of styfane,styrene derivatives, vinyl naphthalene, vinyl naphthalene derivatives,aliphatic alcohol esters of α,β-ethylenically unsaturated carboxylicacids, as well as acrylic acid, acrylic acid derivatives, maleic acid,maleic acid derivatives, itaconic acid, itaconic acid derivatives,fumaric acid, fumaric acid derivatives, vinyl acetate, vinylpyrrolidone,acrylamide and derivatives of these. Natural resins such as rosin,shellac and starch may also be used. These natural resins arealkali-soluble resins capable of being dissolved in an aqueous solutioncomprising a base dissolved therein.

The water-soluble resin described above may preferably be contained inan amount ranging from 0.1 to 5% by weight based on the total weight ofthe ink. It is more preferable for the ink to be prepared in neutralityor alkalinity as a whole. This is preferable for improving thesolubility of the water-soluble resin and providing an ink having muchsuperior long-term storage stability. In this instance, however, such anink may cause corrosion of various members used in an ink-jet recordingapparatus, and hence it should be adjusted in a pH range of from 7 to10.

A pH adjustor used for such purpose may include, for example, variousorganic amines such as diethanolamine and triethanolamine, inorganicalkali agents including alkali metal hydroxides such as sodiumhydroxide, lithium hydroxide and potassium hydroxide, organic acids andmineral acids.

The pigment and water-soluble resin as described above are dispersed ordissolved in an aqueous medium.

The aqueous medium may preferably include mixed solvents of water andwater-soluble organic solvents.

The water should not be tap water containing various ions, and maypreferably be ion-exchanged water (deionized water).

The water-soluble organic solvent used in mixture with water mayinclude, for example, alkyl alcohols having 1 to 4 carbon atoms, such asmethyl alcohol, ethyl alcohol, n-propyl alcohol, isopropyl alcohol,n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol; amides such asdimethylformamide and dimethylacetamide; ketones or ketoalcohols such asacetone and diacetone alcohol; ethers such as tetrahydrofuran anddioxane; polyalkylene glycols such as polyethylene glycol andpolypropylene glycols; alkylene glycols the alkylene group of which has2 to 6 carbon atoms, such as ethylene glycol, propylene glycol, butyleneglycol, triethylene glycol, thiodiglycol, hexylene glycol and diethyleneglycol; 1,2,6-hexanetriol; glycerol; lower alkyl ethers of polyhydricalcohols, such as ethylene glycol monomethyl or -ethyl ether, diethyleneglycol methyl or ethyl ether and triethylene glycol monomethyl or -ethylether; N-methyl-2-pyrrolidone, 2-pyrrolidone, and1,3-dimethyl-2-imidazolidinone. Of these many water-soluble organicsolvents, polyhydric alcohols such as diethylene glycol and lower alkylethers of polyhydric alcohols such as ethylene glycol monomethyl or-ethyl ether are particularly preferred.

The water-soluble organic solvent in the ink of the present inventionmay usually be contained in an amount ranging from 3 to 50% by weight,and preferably in an amount ranging from 3 to 40% by weight, based onthe total weight of the ink. The water may be in an amount ranging from10 to 90% by weight, and preferably in an amount ranging from 30 to 80%by weight, based on the total weight of the ink.

In the present invention, the hydrazide compound incorporated into theink for cross-linking it with carbonyl groups of the dispersant to forma film of non-volatile components may specifically include adipic aciddihydrazide, oxalic acid dihydrazide, carbohydrazide, polyacrylic acidhydrazide (which are available from Otsuka Chemical Co., Ltd.), andACRONAL (trade name; available from Mitshbishi Yuka Badische Co., Ltd.).

The hydrazide compound may preferably be contained in the ink in anamount of from 0.1 to 10% by weight, and more preferably from 0.5 to 5%by weight. Any of these compounds used in an amount less than 0.1% byweight can not bring about an improvement in rub-off fastness of printsas intended in the present invention. On the other hand, its use in anamount more than 10% by weight may tend to cause ill effects such asclogging of the ejection orifices because of an increase in viscosity ofthe ink.

In addition to the components described above, a surface active agent, adefoamer, an antiseptic and so forth may be optionally added to the inkof the present invention so that the ink can have the desired values ofphysical properties. A commercially available water-soluble dye also maybe added.

The ink of the present invention can be prepared in the following way:First, the pigment is added to an aqueous solution comprised of at leastthe water-soluble resin having carbonyl groups and water, followed bystirring. Thereafter, the pigment is dispersed in the solution by adispersion means described later, optionally followed by centrifugalseparation to obtain a desired dispersion. Next, to the resultingdispersion, the hydrazide compound described above is added, followed bystirring to provide ink. In instances in which the alkali-soluble resinsuch as natural resin is used, it is necessary to add a base in order todissolve the resin.

The base added to the dispersion when the alkali-soluble resin is usedmay preferably include organic amines such as monoethanolamine,diethanolamine, triethanolamine, aminomethylpropanol and ammonia orinorganic bases such as potassium hydroxide and sodium hydroxide.

It is also effective to carry out premixing for 30 minutes or morebefore the aqueous solution containing the pigment is dispersed. Thispremixing enables improvement in wettability of the pigment surface topromote adsorption of resin on the pigment surface.

As for the dispersion means used in the present invention, it may be anyof dispersion machines commonly used, including, for example, a ballmill, a roll mill and a sand mill. In particular, a high-speed sand millis preferred, as exemplified by Super mill, Sand grinder, Beads mill,Agitator mill, Grain mill, Dyno mill, Pearl mill and Coball mill (alltrade names).

In the present invention, a pigment with a desired particle sizedistribution can be obtained by a method in which a tumbling medium ofthe dispersion machine is made to have a small size, the tumbling mediumis used in a large packing fraction, the dispersion is carried out for along time, treated products are slowly discharged, or, after beingpulverized, they are classified using a filter or a centrifugalseparator. Any of these methods may also be used in combination.

As a second ink according to the first embodiment of the ink of thepresent invention, the ink comprises the hydrazide compound, an aqueousmedium, and a dye having at least one carbonyl group as the compoundhaving at least one carbonyl group.

The dye having at least one carbonyl group may include dyes having acarbonyl group, a carboxyl group, an ester bond, an amide bond, a ketonegroup, a urethane bond or the like, as exemplified by various dyes suchas direct dyes, acid dyes, food dyes, basic dyes, reactive dyes,disperse dyes, vat dyes, soluble vat dyes, reactive disperse dyes andoil dyes. Of these dyes, water-soluble dyes are particularly preferredin view of performances of the ink.

The content of the dye in the ink depends on the types of liquid mediumcomponents, the properties required for the ink, and so forth. In usualinstances, the dye may be contained in an amount of approximately from0.2 to 20% by weight, preferably from 0.5 to 10% by weight, and morepreferably from 1 to 5% by weight, based on the total weight of the ink.

As the aqueous medium, the same one as that in the first ink previouslydescribed may be used. In the second ink, the most preferable aqueousmedium is composed of water and at least one organic solvent, where theorganic solvent is at least one water-soluble organic solvent with ahigh boiling point as exemplified by polyhydric alcohols such asdiethylene glycol, triethylene glycol, glycerol, 1,2,6-hexanetriol andthiodiglycol, and 2-pyrrolidone.

The water-soluble organic solvent and the water may be contained in theink each in the same amount as in the case of the first ink.

As the hydrazide compound, the same compounds as those in the first inkcan be used.

In addition to the components described above, various kind ofdispersant, surface active agent, viscosity modifier, surface tensionmodifier, fluorescent brightener and so forth may be optionally added tothe second ink of the present invention.

As the viscosity modifier, polyvinyl alcohol, celluloses, water-solubleresins or the like are suitable. As the surface active agent, all sortsof surface active agents of cationic, anionic and nonionic types can beused. As the surface tension modifier, diethanolamine andtriethanolamine are suitable. Besides, pH adjustors using buffers,antifungal agents, and so forth may also be used.

In the case of inks applied in ink-jet recording in which the ink iselectrostatically charged, a resistivity regulator including inorganicbases such as lithium chloride, ammonium chloride or sodium chloride isadded.

In order to solve the problems of feathering and drying performance ofrecorded matter and penetrability and at the same time improvecompatibility with ink-jet recording heads, the second ink of thepresent invention may preferably be adjusted to have, as physicalproperties of the ink itself, a surface tension of from 30 to 68 dyne/cmand a viscosity of 15 cP or less, and more preferably 5 cP or less, at25° C.

Second Preferred Embodiment: (Embodiment in which a compound havingoxazolyl groups is used)

The ink of the present invention may also comprise a component having anoxazolyl group and a compound having at least one carbonyl group.

Use of the ink of the present embodiment makes it possible to obtainstable recorded images having a superior fixing speed or rub-offfastness and which are free from a decrease in print density. This ispresumably because the compound having oxazolyl groups has theproperties of uniformly dissolving in an aqueous solution and, oncewater has disappeared, reacting with the compound having at least onecarbonyl group. More specifically, it is presumed that component (a)(the compound having oxazolyl groups) in the ink of the presentembodiment is uniformly dissolved in the ink, and, once this ink hasbeen ejected from an ink-jet recording head onto recording paper and hasdried, the oxazolyl group possessed by component (a) and the carboxylgroup possessed by component (b) (the compound having at least onecarbonyl group) combine to form a cross-linked structure, which bringsabout a formation of a film of non-volatile components, whereby animprovement in rub-off fastness of prints can be achieved. It is alsopresumed that the cross-linking reaction uniformly takes place withoutregard to the types of paper, and hence any dependence of print qualityon recording paper can be eliminated.

The component (a) used in the ink of the present embodiment comprises(a-1): a water-soluble resin having an oxazolyl group or (a-2): a fineparticle having oxazolyl groups adsorbed on its outer surface. Thecomponent (a) may include oxazoline type reactive polymers. Theoxazoline type reactive polymers are commercially available, including,for example, K-1000 series and K-2000 series acryl-styrene resins, RPSseries styrene resins and RAS series acrylonitrile-styrene resins,produced by Nippon Shokubai Kagaku Kogyo Co., Ltd.

The water-soluble resin (a-1) refers to, for example, an oxazoline typereactive polymer having one or more oxazolyl groups represented by theformula ##STR7##

The fine particle (a-2) used in the present embodiment may includeorganic particles and inorganic particles without any particularlimitations. Those insoluble in water and capable of being stablydispersed therein are preferred. There are also no particularlimitations on particle diameter. Spherical particles may preferably beused. Stated specifically, the organic fine particles may includeparticles of polystyrene, styrene-acrylate copolymers, polymethylmethacrylate, melamine resins, epoxy resins, silicone resins,benzoguanamine resins, polyamide resins, fluorine resins, and polymersobtained by emulsion polymerization of α,β-unsaturated ethylenicmonomers. The inorganic fine particles may include a large number ofmaterials such as titanium dioxide particles, silica particles andalumina particles. As commercially available products, the organic fineparticles may include MUTICLE series products, available from MitsuiToatsu Chemicals, Inc. ME series products, available from Soken Chemical& Engineering Co., Ltd.; JULIMER MB series products, available fromNihon Junyaku Co., Ltd.; TOSPEARL series products, available fromToshiba Silicone Co., Ltd.; EPOSTAR series products, available fromNippon Shokubai Kagaku Kogyo Co., Ltd.; MICROGEL series products,available from Nippon Paint Co., Ltd.; and FLUON series products,available from Asahi Glass Co., Ltd. The inorganic fine particles mayinclude titania series products, available from Indemitsu Kosan Co.,Ltd.; and aluminum oxide C, available from Nippon Aerosil Co., Ltd.Their particle diameter may, depending on the nozzle diameter of aprinter head used, be approximately from 0.01 to 5 μm, and preferablyfrom 0.05 to 1.0 μm.

The fine particle (a-2) refers to a fine particle having at least oneoxazolyl group adsorbed on its outer surface, as diagrammaticallyrepresented by the formula ##STR8##

This component (a) should preferably be contained in the ink in anamount of from 0.1 to 10% by weight, and more preferably from 0.5 to 5%by weight. Its use in a content less than 0.1% by weight tends to resultin an unsatisfactory improvement in rub-Off fastness of prints. On theOther hand, its use in a content more than 10% by weight tends toslightly cause clogging of ejection orifices because of an increase inviscosity of ink.

The compound (b) having at least one carbonyl group includes (b-1): awater-soluble resin having a carbonyl group and (b-2): a dye having acarbonyl group. Of these, the water-soluble resin (b-1) having acarbonyl group, mainly used in the case of a water-based pigment ink,acts as a dispersant. As the water-soluble resin (b-1), the same ones asthose described in the first embodiment may be used. This water-solubleresin (b-1) should preferably be contained in the ink in an amountranging from 0.1 to 5% by weight.

Of the compound (b) having a carbonyl group, used in the ink of thepresent embodiment, the dye (b-2) having a carbonyl group may includethose having a carbonyl group without any particular limitations, asexemplified by direct dyes, acid dyes, food dyes, basic dyes, reactivedyes, disperse dyes, vat dyes, soluble vat dyes, reactive disperse dyesand oil dyes. Of these dyes, water-soluble dyes are particularlypreferred in view of the performance of the ink.

The content of the dye (b-2) in the ink depends on the propertiesrequired for the ink, and so forth. In usual instances, the dye shouldbe contained in an amount of approximately from 0.2 to 20% by weight,preferably from 0.5 to 10% by weight, and more preferably from 1 to 5%by weight, based on the total weight of the ink.

Pigment (c) is used when the ink of the present embodiment comprises awater-based pigment ink. As the pigment (c), the same ones as thosepreviously described in the first embodiment may be used. It may becontained in the ink in an amount ranging from 1 to 20% by weight, andpreferably from 2 to 12% by weight.

The ink of the present embodiment should preferably be an ink comprisingthe components (a), (b) and (c) detailed above which are dispersed ordissolved in a mixed solvent of water (d) and water-soluble organicsolvent (e). The water (d) and the water-soluble organic solvent (e) maybe the same ones as those described in the first embodiment.

The water (d) should preferably be contained in the ink in an amount offrom 10 to 90% by weight, and preferably from 30 to 80% by weight. Thewater-soluble organic solvent (e) should preferably be contained in theink in an amount of from 3 to 50% by weight, and preferably from 3 to40% by weight.

It is more preferable for the ink to be prepared in neutrality oralkalinity as a whole. This is preferable, for example, for improvingthe solubility of the water-soluble resin (c) and providing an inkhaving much superior long-term storage stability. In this instance,however, such an ink may cause corrosion of various members used inink-jet recording apparatus, and hence it should be adjusted in a pHrange of from 7 to 10. A pH adjustor used therefor may include, forexample, various organic amines such as monoethanolamine, diethanolamineand triethanolamine, inorganic bases such as sodium hydroxide, lithiumhydroxide and potassium hydroxide, and other organic acids and mineralacids.

In addition to the components (a) to (e) described above, variousoptional components may be added to the ink of the present embodiment asoccasion calls. For example, a surface active agent, a defoamer, anantiseptic, a dispersant, a viscosity modifier, a surface tensionmodifier, a fluorescent brightener, a water-soluble dye (including dyeshaving no carboxyl group) and so forth may be added. The viscositymodifier may include polyvinyl alcohol, celluloses and water-solubleresins. The surface active agent may include all sorts of surface activeagents of cationic, anionic and nonionic types. The surface tensionmodifier may include diethanolamine and triethanolamine. Besides, pHadjustors using buffers, antifungal agents, and so forth may also beused. In order to prepare inks applied in ink-jet recording in which theink is electrostatically charged, a resistivity regulator includinginorganic bases such as lithium chloride, ammonium chloride or sodiumchloride may be added.

In order to solve the problems of feathering and drying performance ofrecorded matter and penetrability and at the same time improvecompatibility with ink-jet recording heads, the ink of the presentembodiment may preferably be adjusted to have, as physical properties ofthe ink itself, a surface tension of from 30 to 68 dyne/cm and aviscosity of 15 cP or less, and more preferably 5 cP or less, at 25° C.

The ink of the present embodiment can be prepared by a method in which,in the case of, for example, the dye ink, the respective components arewell mixed and thereafter the pH is optionally adjusted, followed byfiltration under pressure.

In the case of, for example, the water-based pigment ink, it can beprepared in the following way: The pigment (c) is added to an aqueoussolution comprised of at least the water-soluble resin (b-1) and water,followed by stirring. Thereafter, the pigment is dispersed in thesolution by a dispersion means described later, optionally followed bycentrifugal separation to obtain a desired pigment dispersion. Next, tothe resulting dispersion, the resective components described above areadded, followed by stirring. It is also effective to carry out premixingfor 30 minutes or more before the aqueous solution containing thepigment (c) is dispersed. This premixing enables improvement inwattability of the pigment surface to promote adsorption of resin on thepigment surface. As the dispersion means used for dispersion, any ofdispersion machines commonly used can be used, including, for example, aball mill and a sand mill. In particular, a high-speed sand mill ispreferred, as exemplified by Super mill, Sand grinder, Beads mill,Agitator mill, Grain mill, Dyno mill, Pearl mill and Coball mill (alltrade names).

A pigment (c) with a desired particle size distribution can be obtainedby a method in which a tumbling medium of the dispersion machine is madeto have a small size, the tumbling medium is used in a large packingfraction, the dispersion is carried out for a long time, treatedproducts are slowly discharged, or, after being pulverized, they areclassified using a filter or a centrifugal separator. Any of thesemethods may also be used in combination.

When ink-jet recording is carried out using the ink of the presentinvention, it is suitable to use an apparatus in which heat energycorresponding to recording signals is imparted to the ink in a recordinghead so that ink droplets are generated by the action of the heatenergy.

FIGS. 1A, 1B and 2 show examples of the construction of the head, whichis a main component of such an ink-jet recording apparatus. FIG. 1A is apartial cross section of a recording head 13 along its ink flow path,and FIG. 1B is a partial cross section along the line A-B in FIG. 1A.The recording head 13 is formed by bonding a glass, ceramic or plasticplate or the like having a channel 14 through which ink is passed, to aheating head 15 used in thermal recording (the drawing shows a thin-filmhead, to which, however the invention, is not limited).

The heating head 15 is comprised of a protective film 16 formed ofsilicon oxide or the like, aluminum electrodes 17-1 and 17-2, a heatingresistor layer 18 formed of nichrome or the like, a heat accumulatinglayer 19, and a substrate 20 with good heat dissipation properties. Theink 21 reaches an ejection orifice (a minute opening) 22 and a meniscus23 is formed there by a pressure P. Upon application of electric signalsto the electrodes 17-1 and 17-2, heat is abruptly generated at theregion denoted by n in the thermal head 15, so that bubbles aregenerated in the ink 21 coming into contact with this region. Thepressure thus produced thrusts out the meniscus 23 and the ink 21 isejected from the orifice 22 in the form of minute recording drops 24 tofly against a recording medium 25. FIG. 2 is a partial perspective viewof a multi-head comprising the head as shown in FIGS. 1A and 1B,arranged in a large number. The multi-head is prepared by bonding aglass plate 27 having a multi-channel 26, to a heating head 28 similarto the head as illustrated in FIG. 1A.

FIG. 3 is a perspective view to show an example of an ink-jet recordingapparatus in which such a head has been incorporated. In FIG. 3,reference numeral 61 denotes a blade serving as a wiping member in theform of a cantilever, one end of which is a stationary end retained by ablade-retaining member. The blade 61 is provided at the positionadjacent to the region in which a recording head makes a record. In thepresent example, the blade is retained in such a form that it projectsto 1 the course through which the recording head is moved. Referencenumeral 62 denotes a cap, which is provided at the home positionadjacent to the blade 61, and is so constituted that it moves in thedirection perpendicular to the direction in which the recording head ismoved and comes into contact with the face of ejection openings to carryout capping. Reference numeral 63 denotes an ink absorber providedadjoiningly to the blade 61, and, similar to the blade 61, is retainedin such a form that it projects to the course through which therecording head is moved. The above blade 61, cap 62 and absorber 63constitute an ejection restoration assembly 64, where the blade 61 andthe absorber 63 remove the water, dust or the like from the ink ejectionopening face. Reference numeral 65 denotes the recording head having anejection energy generating means and ejects ink to the recording mediumset opposite to the ejection opening face provided with ejectionopenings, to carry out recording. Reference numeral 66 denotes acarriage on which the recording head 65 is mounted so that the recordinghead 65 can be moved. The carriage 66 is slidably associated with aguide shaft 67. Part of the carriage 66 is connected (not shown) with abelt 69 driven by a motor 68. Thus, the carriage 66 can be moved alongthe guide 67 and hence the recording head 65 can be moved from arecording region to a region adjacent thereto.

Reference numeral 51 denotes a paper feeding part from which recordingmediums are inserted, and 52, a paper feed roller driven by a motor (notshown). With such construction, the recording medium is fed to theposition opposite to the ejection opening face of the recording head,and, with the progress of recording, is outputted from a paper outputsection provided with a paper output roller.

In the above constitution, the cap 62 of the head restoration assembly64 is receded from the moving course of the recording head 65 when therecording head 65 is returned to its home position, e.g., aftercompletion of recording, and the blade 61 stands projected to the movingcourse. As a result, the ejection opening face of the recording head 65is wiped. When the cap 62 comes into contact with the ejection openingface of the recording head 65 to carry out capping, the cap 62 is movedin such a way that it projects to the moving course of the recordinghead.

When the recording head 65 is moved from its home position to theposition at which recording is started, the cap 62 and the blade 61 areat the same position as the position where the ejection opening face iswiped. As a result, the ejection opening face of the recording head 65is wiped also at the time of this movement.

The above movement of the recording head to its home position is madenot only at the time of the completion of recording or restoration ofejection, but also when the recording head is moved between recordingregions for the purpose of recording, during which it is moved to thehome position adjacent to each recording region at given intervals,where the ejection opening face is wiped in accordance with thismovement.

FIG. 4 is a cross-sectional view to show an example of an ink cartridge,denoted as 45, that has held the ink being fed to the head through anink-feeding tube. Herein reference numeral 40 denotes a bag that hasheld the feeding ink. The top thereof is provided with a stopper 42 madeof rubber. A needle (not shown) may be inserted into this stopper 42 sothat the ink in the ink holder 40 can be fed to the head. Referencenumeral 44 denotes an absorber that receives a waste ink.

The ink-jet recording apparatus used in the present invention is notlimited to the apparatus as described above in which the head and theink cartridge are separately provided, and a device can also bepreferably used in which these are integrally formed as shown in FIG. 5.In FIG. 5, reference numeral 70 denotes an ink cartridge (a recordingunit), in the interior of which an ink absorber impregnated with ink isheld. The ink cartridge is so constructed that the ink in such an inkabsorber is ejected in the form of ink droplets from a head 71 having aplurality of orifices. Reference numeral 72 denotes an air path openingthrough which the interior of the cartridge is made to communicate withthe atmosphere. This ink cartridge 70 can be used in place of therecording head 65 shown in FIG. 3, and is detachably mounted to thecarriage 66.

EXAMPLES

The present invention will be described below by giving Examples andComparative Examples. In the following, "part(s)" indicates "part(s) byweight" unless particularly noted.

First Embodiment Example 1

(1) Preparation of ink:

a. Preparation of pigment dispersion:

    ______________________________________                                        Styrene/acrylic acid/ethyl acrylate copolymer                                                          1.5    parts                                         (acid value: 140; weight average molecular                                    weight: 5,000)                                                                Monoethanolamine         1      part                                          Ion-exchanged water      81.5   parts                                         Diethylene glycol        5      parts.                                        ______________________________________                                    

The above components were mixed, and the mixture was heated to 70° C. ona water bath to completely dissolve the resin component. To theresulting solution, 10 parts of carbon black (MCF88, available fromMitsubishi Chemical Industries Limited) and 1 part of isopropyl alcoholwere added, followed by premixing for 30 minutes, and thereafter themixture obtained was dispersed under conditions shown below.

Dispersion machine: Sand grinder (manufactured by Igarashi Kikai K.K.)

Tumbling media: Zirconium beads of 1 mm diameter

Tumbling media packing fraction: 50% (by volume)

Pulverizing time: 3 hours.

Centrifugal separation was further carried out (12,000 rpm; for 20minutes) to remove coarse particles. Thus, dispersion 1 was formed.

b. Preparation of ink:

    ______________________________________                                        Dispersion 1              30    parts                                         Glycerol                  10    parts                                         Ethylene glycol           5     parts                                         N-methylpyrrolidone       5     parts                                         Ethyl alcohol             2     parts                                         Adipic acid dihydrazide (available from Otsuka                                                          2     parts                                         Chemical Co., Ltd.)                                                           Ion-exchanged water       46    parts.                                        ______________________________________                                    

The above components were mixed to obtain an ink.

(2) Recording:

The ink formulated as shown above was tested using an ink-jet recordingapparatus having an on-demand type multi-recording head capable ofimparting heat energy corresponding to recording signals to therebyeject ink droplets.

Example 2

(1) Preparation of ink:

a. Preparation of pigment dispersion:

    ______________________________________                                        Styrene/maleic acid/maleic acid half ester                                                               4     parts                                        copolymer (acid value: 70; weight average molecular                           weight: 12,000)                                                               Aminomethyl propanol       2     parts                                        Ion-exchanged water        74    parts                                        Diethylene glycol          5     parts.                                       ______________________________________                                    

The above components were mixed, and the mixture was heated to 70° C. ona water bath to completely dissolve the resin component. To theresulting solution, 15 parts of carbon black (MCF88, available fromMitsubishi Chemical Industries Limited) was added, followed by premixingfor 30 minutes, and thereafter the mixture obtained was dispersed underconditions shown below.

Dispersion machine: Pearl mill (manufactured by Ashizawa K.K.)

Tumbling media: Glass beads of 1 mm diameter

Tumbling media packing fraction: 50% (by volume)

Discharge rate: 100 ml/min.

Centrifugal separation was further carried out (12,000 rpm; for 20minutes) to remove coarse particles. Thus, dispersion 2 was formed.

b. Preparation of ink:

    ______________________________________                                        Dispersion 2              30    parts                                         Glycerol                  8     parts                                         Ethylene glycol           5     parts                                         Ethanol                   5     parts                                         Oxalic acid dihydrazide (available from Otsuka                                                          1     part                                          Chemical Co., Ltd.)                                                           Ion-exchanged water       51    parts.                                        ______________________________________                                    

The above components were mixed, and aminomethyl propanol was added toadjust the pH value to 8 to 10.

(2) Recording:

The ink thus formulated was tested in the same manner as in Example 1.

Example 3

(1) Preparation of ink:

a. Preparation of pigment dispersion:

    ______________________________________                                        α-Methylstyrene/methyl acrylate/acrylic acid                                                     2.0    parts                                         copolymer (acid value: 95; weight average                                     molecular weight: 8,000)                                                      Ion-exchanged water      81.0   parts                                         Ethylene glycol          5      parts.                                        ______________________________________                                    

The above components were mixed, and the mixture was heated to 70° C. ona water bath to completely dissolve the resin component. To theresulting solution, 11 parts of carbon black (S170, available fromDegussa, Inc.) and 1 part of isopropyl alcohol were added, followed bypremixing for 60 minutes, and thereafter the mixture obtained wasdispersed under conditions shown below.

Dispersion machine: Sand grinder (manufactured by Igarashi Kikai K.K.)

Tumbling media: Zirconium beads of 0.5 mm diameter

Tumbling media packing fraction: 70% (by volume)

Pulverizing time: 10 hours.

Centrifugal separation was further carried out (12,000 rpm; for 20minutes) to remove coarse particles. Thus, dispersion 3 was formed.

b. Preparation of ink:

    ______________________________________                                        Dispersion 3             30     parts                                         Glycerol                 12     parts                                         Diethylene glycol        10     parts                                         2-Pyrrolidone            5      parts                                         ACRONAL YJ-6380D (trade name; available                                                                0.5    part                                          from Mitshbishi Yuka Badische Co., Ltd.)                                      Ion-exchanged water      42.5   parts.                                        ______________________________________                                    

The above components were mixed to obtain an ink.

(2) Recording:

The ink thus formulated was tested in the same manner as in Example 1.

Comparative Examples 1 to 3

Examples 1 to 3 were respectively repeated to prepare inks, except thatno hydrazide compound was added and ion-exchanged water was insteadadded. Using inks thus obtained, recording tests were carried out in thesame manner as in Examples 1 to 3.

Evaluation of ink and prints:

Prints obtained by printing characters on Canon NP-DRY copy paperaccording to the above method were evaluated in the following way.Results obtained are shown in Table 1.

(1) Print density of prints:

Print density of prints was measured using a Macbeth densitometer(TR918).

(2) Ink drying time:

Printed areas were rubbed with filter paper (trade name: No.5C;available from Toyo Roshi K.K.), and the time taken until the printedareas no longer blurred was measured.

(3) Rub-off fastness:

Prints were rubbed with a highlighter pen. An instance in which noprints blurred when rubbed 5 times was evaluated as "A"; an instance inwhich prints blurred in 5 times but no print blurred when rubbed 3times, as "B"; and an instance in which prints blurred when rubbed once,as "C".

                  TABLE 1                                                         ______________________________________                                                Print  Drying time (sec)                                                                             Rub-off                                                density                                                                              Solid print                                                                             Characters                                                                              fastness                                   ______________________________________                                        Example:                                                                      1         1.40     30        10      A                                        2         1.38     32.5      12.5    A                                        3         1.37     35        15      A                                        Comparative                                                                   Example:                                                                      1         1.30     60        35      C                                        2         1.29     65        40      C                                        3         1.29     75        45      C                                        ______________________________________                                    

Examples 4 to 9

To prepare inks A to F, components as respectively shown below weremixed and stirred for 5 hours. Thereafter, an aqueous 0.1% sodiumhydroxide solution was added to adjust the pH to 7.5, followed byfiltration under pressure using a membrane filter with a pore size of0.22 μm (trade name: Fluoro pore filter; available from SumitomoElectric Industries, Ltd.). Thus, inks A to F of the present inventionwere obtained.

Composition of ink A:

    ______________________________________                                        C.I. Direct Yellow 44   2       parts                                         Diethylene glycol       15      parts                                         Adipic acid dihydrazide 3       parts                                         (available from Otsuka Chemical Co., Ltd.)                                    Water                   80      parts.                                        Composition of ink B:                                                         C.I. Direct Red 26      2       parts                                         Glycerol                10      parts                                         Ethylene glycol         5.5     parts                                         Oxalic acid dihydrazide 2       parts                                         (available from Otsuka Chemical Co., Ltd.)                                    Water                   80.5    parts.                                        Composition of ink C:                                                         C.I. Food Black 1       3       parts                                         Triethylene glycol      10      parts                                         N-methyl-2-pyrrolidone  3       parts                                         Carbohydrazide          1       part                                          (available from Otsuka Chemical Co., Ltd.)                                    Water                   83      parts.                                        Composition of ink D:                                                         C.I. Direct Blue 149    2.5     parts                                         1,2,6-Hexanetriol       5       parts                                         Diethylene glycol       10      parts                                         ACRONAL YJ-63680D       3       parts                                         (trade name; available from Mitshbishi Yuka                                   Badische Co., Ltd.)                                                           Water                   79.5    parts.                                        Composition of ink E:                                                         HI12286 (available from ICI)                                                                          2       parts                                         Thiodiglycol            6       parts                                         Diethylene glycol       9       parts                                         Adipic acid dihydrazide 3       parts                                         (available from Otsuka Chemical Co., Ltd.)                                    ACETYLENOL EH           0.5     part                                          (trade name; available from Kawaken Fine                                      Chemicals Co., Ltd.)                                                          Water                   79.5    parts.                                        Composition of ink F:                                                         C.I. Acid Green 34      3       parts                                         Ethylene glycol         8       parts                                         Diethylene glycol       7       parts                                         Oxalic acid dihydrazide 1       part                                          (available from Otsuka Chemical Co., Ltd.)                                    Ethylene glycol monobutyl ether                                                                       1       part                                          Water                   80      parts.                                        ______________________________________                                    

Comparative Examples 4 to 9

Inks G to L were prepared in the same manner as in Examples 4 to 9,respectively, except that no hydrazide compound was used.

Using the inks prepared in Examples 4 to 9 and Comparative Examples 4 to9, recording was carried out to obtain prints, which were then evaluatedin the following way. Results obtained are shown together in Table 2.

(1) Evaluation of drying time:

Characters were printed on commercially available copy paper and bondpaper, and the printed areas were rubbed with filter paper (trade name:No.5C; available from Toyo Roshi K.K.) after 5 seconds, 10 seconds, 20seconds and 30 seconds. Evaluation was made in the following way. Theevaluation was made in an environment of 25° C., 60% RH.

AA: No blur when rubbed after 5 seconds

A: No blur when rubbed after 10 seconds

B: No blur when rubbed after 20 seconds

C: Blurred when rubbed after 30 seconds

(2) Occurrence of blurring:

To examine the occurrence of blurring, 300 dots were continuouslyprinted using a printer on commercially available copy paper and bondpaper in a manner such that they did not touch one another, and wereleft to stand for 1 hour or more. Thereafter, the number of dots havingcaused blurring was counted on a microscope, and its proportion to thewhole dot number was indicated in % to make an evaluation in thefollowing way. The evaluation was made in an environment of 25° C., 60%RH.

A: 10% or less

B: 11 to 30%

C: 31% or more

(3) Anti-clogging:

Anti-clogging refers to the lack of clogging of ejection orifices thatmay occur when printing is again started after a pause. The ink holderof a printer was filled with a given ink and alphabet and numeralcharacters were continuously printed for 10 minutes. Thereafter,printing was stopped and the printer was left to stand for 10 minutes inan uncapped state and thereafter alphabet and numeral characters wereprinted, where any faulty prints such as blurred or broken characterswere examined to make an evaluation. The evaluation was made in anenvironment of 25° C., 60% RH.

A: No faulty prints occur on the first and subsequent characters.

B: Characters partly blur or break from the first.

C: Characters can not be printed at all from the first.

(4) Frequency response:

Resulting prints were observed with the naked eye to examine the stateof prints, i.e., any blurs or blank areas and defective ink-dropletimpact such as a splash or slippage, and an evaluation was made in thefollowing way.

AA: Ink continuity to frequencies is good, and no blurs or white areasand defective ink-droplet impact are seen in both solid prints andcharacter prints.

A: Ink continuity to frequencies is substantially good, and no blurs orwhite areas and defective ink-droplet impact are seen in characterprints, but blurs are slightly seen in solid prints.

B: No blurs or white areas are seen in character prints, but a defectiveink-droplet impact is partly seen. In solid prints, blurs or white areasare seen in about 1/3 of the solid prints.

C: Many blurs or white areas are seen in solid prints, and blurs ordefective ink-droplet impact are seen in a large number in characterprints.

                  TABLE 2                                                         ______________________________________                                                                             Fre-                                             Drying time                                                                             Blurring    Anti-  quency                                             Copy    Bond    Copy  Bond  clog-                                                                              re-                                Ink       paper   paper   paper paper ging sponse                             ______________________________________                                        Example:                                                                      4      (A)    A       A     A     A     A    A                                5      (B)    A       A     A     A     A    A                                6      (C)    A       A     A     A     A    A                                7      (D)    A       A     A     A     A    A                                8      (E)    AA      AA    A     A     A    A                                9      (F)    AA      AA    A     A     A    A                                Com-                                                                          parative                                                                      Example:                                                                      4      (G)    C       B     B     B     B    B                                5      (H)    B       B     B     B     B    B                                6      (I)    B       B     B     B     B    B                                7      (J)    B       B     B     B     B    B                                8      (K)    AA      AA    C     C     A    A                                9      (L)    AA      AA    C     C     A    A                                ______________________________________                                    

As described above, the use of the ink according to the presentinvention brings about an improvement in rub-off fastness of prints andfixing speed, and also can eliminate any uneven print densitiesascribable to the types of recording paper, making it possible to obtainstable recorded images. The ink is also effective for solving variousproblems without causing the deterioration of performances such asejection stability of the ink, anti-clogging at head tips andmaintenance of print quality.

The ink of the present invention enables good recording free fromblurring, with a superior quality level and with a good fixingperformance also on plain paper such as paper for copying, paper forreporting, notepaper, letter paper, bond paper and computer printoutpaper commonly used in offices and so forth.

The present invention also makes it possible to obtain an ink with goodsafety even in its use in offices and homes.

Second Embodiment

The second embodiment will be described below by giving Examples 10 to12 and Comparative Examples 10 to 12 relating to water-based pigmentinks.

Example 10

Preparation of pigment dispersion:

    ______________________________________                                        Styrene/acrylic acid/ethyl acrylate copolymer                                                           1.5    parts                                        (acid value: 140; weight average molecular weight:                            5,000)                                                                        Monoethanolamine          1      part                                         Ion-exchanged water       81.5   parts                                        Diethylene glycol         5      parts.                                       ______________________________________                                    

The above components were mixed, and the mixture was heated to 70° C. ona water bath to completely dissolve the resin component. To theresulting solution, 10 parts of carbon black (MCF88, available fromMitsubishi Chemical Industries Limited) and 1 part of isopropyl alcoholwere added, followed by premixing for 30 minutes, and thereafter themixture obtained was dispersed. In this dispersion treatment, Sandgrinder (manufactured by Igarashi Kikai K.K.) was used as a dispersionmachine, where zirconium beads of 1 mm diameter were used as thetumbling media in a tumbling media packing fraction of 50% by volume,and pulverization was carried out for 3 hours. Centrifugal separationwas further carried out at 12,000 rpm for 20 minutes to remove coarseparticles. Thus, a dispersion was formed.

Preparation of ink:

    ______________________________________                                        Pigment dispersion shown above                                                                         30     parts                                         Glycerol                 10     parts                                         Ethylene glycol          5      parts                                         N-methylpyrrolidone      5      parts                                         Ethyl alcohol            2      parts                                         K-1010E (trade name; available from Nippon                                                             2      parts                                         Shokubai Kagaku Kogyo Co., Ltd.)                                              Ion-exchanged water      46     parts.                                        ______________________________________                                    

The above components were mixed to obtain an ink.

Example 11

Preparation of pigment dispersion:

    ______________________________________                                        Styrene/maleic acid/maleic acid half ester                                                               4     parts                                        copolymer (acid value: 70; weight average molecular                           weight: 1,200)                                                                Aminomethyl propanol       2     parts                                        Ion-exchanged water        74    parts                                        Diethylene glycol          5     parts.                                       ______________________________________                                    

The above components were mixed, and the mixture was heated to 70° C. ona water bath to completely dissolve the resin component. To theresulting solution, 15 parts of carbon black (MCF88, available fromMitsubishi Chemical Industries Limited) was added, followed by premixingfor 30 minutes, and thereafter the mixture obtained was dispersed. Inthis dispersion treatment, Pearl mill (manufactured by Ashizawa K.K.)was used as a dispersion machine, where glass beads of 1 mm diameterwere used as tumbling media in a tumbling media packing fraction of 50%by volume under a discharge rate of 100 ml/min. Centrifugal separationwas further carried out at 12,000 rpm for 20 minutes to remove coarseparticles. Thus, a dispersion was formed.

Preparation of ink:

    ______________________________________                                        Pigment dispersion shown above                                                                         30     parts                                         Glycerol                 8      parts                                         Ethylene glycol          5      parts                                         Ethanol                  5      parts                                         RPS-1001 (trade name; available from Nippon                                                            1      part                                          Shokubai Kagaku Kogyo Co., Ltd.)                                              Ion-exchanged water      51     parts.                                        ______________________________________                                    

The above components were mixed, and aminomethyl propanol was added toadjust the pH value to 8 to 10. Thus, an ink was obtained.

Example 12

Preparation of pigment dispersion:

    ______________________________________                                        Preparation of pigment dispersion:                                            ______________________________________                                        α-Methylstyrene/methyl acrylate/acrylic acid                                                     2.0    parts                                         copolymer (acid value: 95; weight average                                     molecular weight: 8,000)                                                      Ion-exchanged water      81.0   parts                                         Ethylene glycol          5      parts.                                        ______________________________________                                    

The above components were mixed, and the mixture was heated to 70° C. ona water bath to completely dissolve the resin component. To theresulting solution, 11 parts of carbon black (S170, available fromDegussa, Inc.) and 1 part of isopropyl alcohol were added, followed bypremixing for 60 minutes, and thereafter the mixture obtained wasdispersed. In this dispersion treatment, Sand grinder (manufactured byIgarashi Kikai K.K.) was used as a dispersion machine, where zirconiumbeads of 0.5 mm diameter were used as tumbling media in a tumbling mediapacking fraction of 70% by volume, and pulverization was carried out for100 hours. Centrifugal separation was further carried out at 12,000 rpmfor 20 minutes to remove coarse particles. Thus, a dispersion wasformed.

Preparation of ink:

    ______________________________________                                        Pigment dispersion shown above                                                                          30     parts                                        Glycerol                  12     parts                                        Diethylene glycol         10     parts                                        2-Pyrrolidone             5      parts                                        CX-K2010E (trade name; available from Nippon                                                            0.5    part                                         Shokubai Kagaku Kogyo Co., Ltd.)                                              Ion-exchanged water       42.5   parts.                                       ______________________________________                                    

The above components were mixed to obtain an ink.

Comparative Examples 10 to 12

Examples 10 to 12 were respectively repeated to prepare inks, exceptthat no compound having an oxazolyl group was added and ion-exchangedwater was instead added in the same amount.

Evaluation of ink:

Using each ink, characters were printed on copy paper (NP-DRY copypaper, available from Canon Inc.) using an ink-jet recording apparatushaving an on-demand type multi-recording head capable of imparting heatenergy corresponding with recording signals to thereby eject inkdroplets. The print density, drying time and rub-off fastness of printswere evaluated in the same manner as in Examples 1 to 3. Resultsobtained are shown in Table 3.

                  TABLE 3                                                         ______________________________________                                                Print  Drying time (sec)                                                                             Rub-off                                                density                                                                              Solid print                                                                             Characters                                                                              fastness                                   ______________________________________                                        Example:                                                                      10        1.40     30        10      A                                        11        1.38     32.5      12.5    A                                        12        1.39     32.5      12.5    A                                        Comparative                                                                   Example:                                                                      10        1.30     60        35      C                                        11        1.29     70        40      C                                        12        1.29     75        45      C                                        ______________________________________                                    

As is seen from the results shown in Table 3, the inks of Examples 10 to12, compared with the inks of Comparative Examples 10 to 12, showsuperior print density, drying time and rub-off fastness because of thecompound having oxazolyl groups contained therein.

The second embodiment will be further described below by giving Examples13 to 18 and Comparative Examples 13 to 18 relating to dye inks.

Examples 13 to 18

Components respectively shown below were mixed and stirred for 5 hours.Thereafter, a 0.1% sodium hydroxide aqueous solution was added to adjustthe pH value to 7.5, followed by filtration under pressure using amembrane filter with a pore size of 0.22 μm (trade name: Fluoro porefilter; available from Sumitomo Electric Industries, Ltd.). Thus, inksof the present invention were obtained.

    ______________________________________                                        (Example 13)                                                                  C.I. Direct Yellow 41    2      parts                                         Diethylene glycol        15     parts                                         K-1010E                  3      parts                                         (trade name; available from Nippon Shokubai                                   Kagaku Kogyo Co., Ltd.)                                                       Ion-exchanged water      80     parts.                                        (Example 14)                                                                  C.I. Direct Black 51     3      parts                                         Triethylene glycol       10     parts                                         N-methyl-2-pyrrolidone   3      parts                                         RPS-1001                 1      part                                          (trade name; available from Nippon Shokubai                                   Kagaku Kogyo Co., Ltd.)                                                       Ion-exchanged water      83     parts.                                        (Example 15)                                                                  C.I. Direct Blue 149     2.5    parts                                         1,2,6-Hexanetriol        5      parts                                         Diethylene glycol        10     parts                                         CX-K2010E                3      parts                                         (trade name; available from Nippon Shokubai                                   Kagaku Kogyo Co., Ltd.)                                                       Ion-exchanged water      79.5   parts.                                        (Example 16)                                                                  HI12286 (available from ICI Co.)                                                                       2      parts                                         Thiodiglycol             6      parts                                         Diethylene glycol        9      parts                                         K-1020E                  3      parts                                         (trade name; available from Nippon Shokubai                                   Kagaku Kogyo Co., Ltd.)                                                       ACETYLENOL EH            0.5    parts                                         (trade name; available from Kawaken Fine                                      Chemicals Co., lTd.)                                                          Ion-exchanged water      79.5   parts.                                        (Example 17)                                                                  C.I. Direct Black 174    3      parts                                         Ethylene glycol          8      parts                                         Diethylene glycol        7      parts                                         RAS-1005                 1      part                                          (trade name; available from Nippon Shokubai                                   Kagaku Kogyo Co., Ltd.)                                                       Ethylene glycol monobutyl ether                                                                        1      part                                          Ion-exchanged water      80     parts.                                        (Example 18)                                                                  C.I. Acid Green 34       3      parts                                         Ethylene glycol          8      parts                                         Triethylene glycol       7      parts                                         K-10120E                 3      parts                                         (trade name; available from Nippon Shokubai                                   Kagaku Kogyo Co., Ltd.)                                                       Triethylene glycol monobutyl ether                                                                     1      part                                          Ion-exchanged water      78     parts.                                        ______________________________________                                    

Comparative Examples 13 to 18

Examples 13 to 18 were respectively repeated to prepare inks, exceptthat no compound having an oxazolyl group was added and ion-exchangedwater was instead added in the same amount.

Evaluation of ink:

Each ink was poured into an ink cartridge for an ink-jet printer (tradename: BJ-10V, manufactured by Canon Inc.) making use of a heatingelement as an energy source for ink ejection. Using this printer,recording was carried out on commercially available copy paper and bondpaper. Drying time of prints, occurrence of blurring, anti-clogging andfrequency response were evaluated in the same manner as in Examples 4 to9. Results obtained are shown in Table 4.

                  TABLE 4                                                         ______________________________________                                               Drying time                                                                             Blurring    Anti-  Fre-                                             Copy  Bond    Copy    Bond  clog-                                                                              quency                                       paper paper   paper   paper ging response                              ______________________________________                                        Example:                                                                      13       A       A       A     A     A    A                                   14       A       A       A     A     A    A                                   15       A       A       A     A     A    A                                   16       AA      AA      A     A     A    A                                   17       AA      AA      A     A     A    A                                   18       AA      AA      A     A     A    A                                   Comparative                                                                   Example:                                                                      13       C       B       B     B     B    B                                   14       B       B       B     B     B    B                                   15       B       B       B     B     B    B                                   16       AA      AA      C     C     B    B                                   17       AA      AA      C     C     A    A                                   18       AA      AA      C     C     A    A                                   ______________________________________                                    

As is seen from the results shown in Table 4, the inks of Examples 13 to18, compared with the inks of Comparative Examples 13 to 18, showsuperior drying time, occurrence of blurring, anti-clogging andfrequency response because of the compound having an oxazolyl groupcontained therein. As described above, ink-jet recording carried outusing the ink of the present invention can bring about recorded imagesfree from uneven print quality level due to differences in recordingpaper, having superior drying time and rub-off fastness and free from adecrease in print density and blurring. Since also it is unnecessary toadd highly viscous organic solvents as in the prior art, stablerecording can be performed without causing the problems of ink ejectionstability and solidification at head tips.

Thus, the ink of the present invention enables good recording also onplain paper such as paper for copying, paper for reporting, notepaper,letter paper, bond paper and computer printout paper commonly used.

What is claimed is:
 1. An ink suitable for an ink-jet system, whichcomprises a pigment, an aqueous medium, a water-soluble resin having atleast one carbonyl group and a hydrazide compound selected from thegroup consisting of a styrene-maleic acid resin having at least twohydrazide groups, a polyacrylic acid having at least two hydrazidegroups and a compound of the formula ##STR9## wherein R represents(--CH₂ --)_(n) or C₆ H₄, wherein n is an integer of 0 to 10, or of theformula ##STR10## and has a viscosity of not more than 15 cP at 25° C.2. An ink suitable for an ink-jet system, which comprises a dye havingat least one carbonyl group, an aqueous medium and a hydrazide compoundselected from the group consisting of a styrene-maleic acid resin havingat least two hydrazide groups, a polyacrylic acid having at least twohydrazide groups and a compound of the formula ##STR11## wherein Rrepresents (--CH₂ --)_(n) or C₆ H₄, where n is an integer of 0 to 10, orof the formula ##STR12## and has a viscosity of not more than 15 cP at25° C.
 3. The ink according to claim 1 or 2, wherein said hydrazidecompound is contained in an amount ranging from 0.1 to 10% by weightbased on the total weight of the ink.
 4. The ink according to claim 1,wherein said water-soluble resin is contained in an amount ranging from0.1 to 5% by weight based on the total weight of the ink.
 5. The inkaccording to claim 1, wherein said water-soluble resin has a weightaverage molecular weight ranging from 1,000 to 30,000.
 6. The inkaccording to claim 2, wherein said dye is contained in an amount rangingfrom 0.2 to 20% by weight based on the total weight of the ink.
 7. Theink according to claim 1 or 2, wherein said aqueous medium compriseswater and a water-soluble organic solvent.
 8. The ink according to claim1 or 2, wherein said ink-jet system is a system in which thermal energyis applied to the ink.
 9. The ink according to claim 2, wherein said dyeis contained in an amount ranging from 0.5 to 10% by weight based on thetotal weight of the ink.
 10. The ink according to claim 1, wherein saidpigment is contained in an amount ranging from 1 to 20% by weight basedon the total weight of the ink.
 11. The ink according to claim 1,wherein said pigment is contained in an amount ranging from 2 to 12% byweight based on the total weight of the ink.
 12. The ink according toclaim 1 or 2, wherein said hydrazide compound is contained in an amountranging from 0.5 to 5% by weight based on the total weight of the ink.13. The ink according to claim 1 or 2, wherein said viscosity is notmore than 5 cP at 25° C.
 14. The ink according to claim 1 or 2, whereinsaid ink has a surface tension ranging from 30 to 68 dyn/cm.